Merge bitcoindevkit/bdk-cli#241: chore: remove remainig MSRV mentions

4347ea24341a18c978747771c9c09f27a6fcc1aa chore: clippy fixes (Vadim Anufriev)
09b5b3b99b7bab8c228af458f7978fb996507478 chore: remove remainig msrv mentions (Vadim Anufriev)

Pull request description:

  Relates #211.

  ### Description

  I noticed that we still have mentions of MSRV, despite the fact that MSRV was removed in #211.
  In this PR I'm removing the found mentions.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  tvpeter:
    ACK 4347ea24341a18c978747771c9c09f27a6fcc1aa
  notmandatory:
    ACK 4347ea24341a18c978747771c9c09f27a6fcc1aa

Tree-SHA512: 6a3d8efcf7e70ebf5b5dce2e49eba5af41ef6cb22052db78dd3b00e77052b746285d55cd8b571a914f7d3e0b926382be220fe8a0a1d225366c6075a38cf752fa